Laser powder bed fusion (LPBF) additive manufacturing has been advancing in the fabrication of metallic multi-material structures with intricate structures and refined material layouts. Herein, a comprehensive review of the recent achievements of multi-material structures via LPBF is provided in terms of interface characteristics and strengthening methods, critical technical issues and potential applications. It begins with the introduction of multi-material structures and the scope of the review. The interface characteristics (including representative multi-material types printed by LPBF, interfacial microstructure, defects, etc.) and strengthening methods of multi-material structures are then presented. Thereafter, the critical technical issues in LPBF for multi-material structures are discussed with regard to equipment development, data preparation, thermodynamic calculation and process simulation, and powder cross-contamination and recycling. Moreover, the potential applications (particularly in biomedical, electronic, aerospace) are illustrated and discussed. Finally, the outlook is outlined to provide guidance for future research.

A nickel–titanium (NiTi)-based intermetallic coating was in-situ synthesized on a Ti–6Al–4V (TC4) substrate via laser melting deposition (LMD) using Ni–20Cr and TC4 powders. Scanning electron microscopy, X-ray diffraction, a digital microhardness tester and an electrochemical analyzer were used to evaluate the microstructure, Vicker’s microhardness and electrochemical corrosion resistance of the intermetallic coating. Results indicate that the microstructure of the intermetallic coating is composed of NiTi₂, NiTi and Ni₃Ti. The measured microhardness achieved is as high as ~850 HV_0.2, ~2.5 times larger than that of the TC4 alloy, which can be attributed to the solid solution strengthening of Al and Cr, dispersion strengthening of the intermetallic compounds, and grain refinement strengthening from the rapid cooling of LMD. During the electrochemical corrosion of 3.5% NaCl solution, a large amount of Ti ions were released from the intermetallic coating surface and reacted with Cl⁻ ions to form [TiCl₆]² with an increase in corrosion voltage. In further hydrolysis reactions, TiO₂ formation occurred when the ratio of [TiCl₆]²⁻ reached a critical value. The in-situ synthesized intermetallic coating can achieve a superior corrosion resistance compared to that of the TC4 alloy.